Bar codes are commonly known in various forms and are characterized by their capability of recording information which can be recovered by a single pass along a line by a scanning device. Typically, bar codes are a series of vertical marks which carry information by their varying widths, by the varying spacing between marks, or by both.
The dimensions of bar codes in the direction perpendicular to the scan have significance generally only to assure that the scan observes the code. Typically, positioning of the scanner can be assured only within a certain range of accuracy and the perpendicular dimension of the bar code must be at least broad enough to assure that the scanner observes the code when it is positioned anywhere within the range of accuracy. The positioning of the scanner can be so variable that the bar code must be quite broad.
To reduce the breadth of bar code and the consequent space used for recording, it is desirable to improve the precision of positioning the scanner. It is known generally in the scanning art to employ a separate mark as a guide or alignment reference which is sensed by the scanner and from which position the scanner is more precisely positioned with respect to the code to be sensed.
Where such an alignment mark is preprinted or printed in some manner not integral with recording the bar code information, such a use of an alignment or register mark is believed to be conventional and within the state of the art. U.S. Pat. No. 3,433,933 to Hardin is exemplary of such prior art. It teaches a narrow vertical line as an alignment mark, which is sensed to define a scan line through a column containing horizontal marks. The alignment mark in the preferred form of the instant invention is relatively wide. Although no direct alignment occurs off the mark in the following publication, it is cited because it differs from the cited patent in that the mark is relatively wide. That publication is the following: "Optical Mark Sensing of Single-Color Documents", by W. B. Plummer, IBM Technical Disclosure Bulletin, Vol. 19, No. 8, January 1977 at page 3174.
Other patents similar in use of alignments marks to the Hardin patent cited above could be mentioned, but they are considered less pertinent in that they involve the reading of alphabet symbols and the like. The instant subject matter differs fundamentally from known prior art in that the alignment mark is printed with the printing of the code information. In the preferred mode, rather than being a narrow line, the alignment mark is both substantially wide and thick. With the printing of the alignment mark prior to but with the printer to print bar code, the instant subject matter employs a scanning of the alignment mark to define a relationship between the printer and the scanner subsequently used to position the print head for re-reading printed code for errors.